High-speed optical delay generating method by rotation reflector in optical coherence tomography and optical coherence tomography device

ABSTRACT

A high-speed optical delay generating method by a rotation reflector in optical coherence tomography, capable of providing a sectional picture with a sufficiently long depth-direction (Z direction) scanning distance, and an optical coherence tomography device therefor are provided. The device comprises a low-coherence light source ( 1 ), a half mirror ( 2 ) for splitting light from the low-coherence light source ( 1 ) into two, that is, into object light towards an object (A) to be examined and reference light, a light delay mechanism ( 3 ) for delaying the reference light by means of a rotation reflector ( 12 ), a fixed mirror ( 4 ) for reflecting/returning the reference light from the light delay mechanism ( 3 ), the half-mirror ( 2 ) for combining the object light returning from the object (A) to be examined with the reference light returning from the light delay mechanism, and a light detector ( 11 ) for detecting interference light including a heterodyne interference beat signal combined at the half mirror ( 2 ).

TECHNICAL FIELD

The present invention relates to a high-speed optical delay generatingmethod by a rotation reflector in optical coherence tomography, and toan optical coherence tomography device therefor.

BACKGROUND ART

As a conventional high-speed optical delay generating method in opticalcoherence tomography, a method has been known, in which the light-pathfor reference light extends through a half mirror, a first mirror, asecond mirror, and the half mirror, and the boundary between the firstmirror and the second mirror is set to be the reflection center.

FIG. 1 schematically shows the configuration of a conventional opticalcoherence tomography device. This figure shows a low-coherence lightsource (e.g., an SLD (super luminescent diode) light source) 101, a halfmirror (two-splitting half mirror) 102, a rotating member 103, a firstmirror 104A, a second mirror 104B, mirrors 105 and 106, an object A tobe examined, and a light detector 107.

DISCLOSURE OF INVENTION

However, according to the above-described conventional high-speedoptical delay generating method in optical coherence tomography, thereflection optical axis is shifted with respect to the incident opticalaxis, depending on the rotation angle, whenever scanning is carried outin the depth direction (Z direction). Thus, heterodyne interference beatsignals combined at the two-splitting half mirror can be obtained onlyin a very small angular range.

Accordingly, the optical coherence tomography device using theconventional high-speed optical delay generating method in opticalcoherence tomography has a problem in that only cross-sectional pictureshaving a very short scanning-distance in the depth direction (Zdirection) can be provided.

In view of the foregoing, it is an object of the present invention toprovide a high-speed optical delay generating method by a rotationreflector in optical coherence tomography, capable of providing asectional picture with a sufficiently long depth-direction (Z direction)scanning distance, and an optical coherence tomography device therefor.

To achieve the object of the present invention:

[1] a high-speed optical delay generating method by a rotation reflectorin optical coherence tomography comprises splitting light from alow-coherence light source into two, that is, into object light towardsan object to be examined and reference light by means of a two-splittinghalf mirror, causing the reference light to be reflected at and returnfrom a fixed mirror via a light delay mechanism containing the rotationreflector to be combined with the object light returning from the objectto be examined at the two-splitting half mirror, and detectinginterference light including a heterodyne interference beat signalcombined at the two-splitting half mirror;

[2] an optical coherence tomography device comprises a low-coherencelight source, a two-splitting half mirror for splitting light from thelow-coherence light source into two, that is, into object light towardsan object to be examined and reference light, a light delay mechanismfor delaying the reference light by means of a rotation reflector, afixed mirror for causing the reference light from the light delaymechanism to be reflected thereat and return therefrom, thetwo-splitting half mirror for combining the object light returning fromthe object to be examined with the reference light returning from thelight delay mechanism, and a light detector for detecting interferencelight including a heterodyne interference beat signal combined at thetwo-splitting half mirror;

[3] an optical coherence tomography device comprises a low-coherencelight source, a two-splitting half mirror for splitting light from thelow-coherence light source into two, that is, into object light towardsan object to be examined and reference light, a light delay mechanismfor delaying the reference light by means of a rotation reflector, afixed mirror for causing the reference light from the light delaymechanism to be reflected thereat and return therefrom, a plane scanningmechanism for scanning an inner plane of the object to be examined withthe object light, an objective lens, the two-splitting half mirror forcombining the object light returning from the object to be examined withthe reference light returning from the light delay mechanism, and alight detector for detecting interference light combined at thetwo-splitting half mirror;

[4] in an optical coherence tomography device according to [2] or [3],the light delay mechanism contains a plurality of pairs of mirrors eachcomprising a first mirror and a second mirror arranged on the surface ofa rotation member, which is rotated at high speed, in a radial directionpattern in such a manner as to cause the light to be reflected in thetangential direction of the rotation member;

[5] in an optical coherence tomography device according to [2] or [3],the fixed mirror is a scanning-starting point adjusting mirror which canadjust the scanning-starting position in the depth direction so as tocorrespond to the Z direction, which is the depth direction of theoptical axis of the object light; and

[6] in an optical coherence tomography device according to [3], theplane scanning mechanism has an X-axis scanning mirror and a Y-axisscanning mirror, and the plane (X-Y) of the object to be examined isscanned at high speed with the object light towards the object to beexamined.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the configuration of a conventional optical coherencetomography device.

FIG. 2 shows the configuration of an optical coherence tomography deviceaccording to an embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the present invention will be described indetail.

FIG. 2 shows the configuration of an optical coherence tomography deviceaccording to an embodiment of the present invention.

In FIG. 2, there are shown a low-coherence light source (e.g., an SLD(super luminescent diode) light source) 1, a half mirror (two-splittinghalf mirror) 2, a light delay mechanism 3, a first mirror 3A, a secondmirror 3B, a scanning-starting point adjusting mirror (fixed mirror) 4,a plane scanning mechanism (X-axis scanning mirror and Y-axis scanningmirror) 5, a dichroic mirror 6 (reflecting visible light andtransmitting infrared light), an objective lens 7, a half mirror 8 for acamera light source, a CCD illumination light source 9, a monitor CCD10, a light detector 11, a rotation member 12, a PC (personal computer)13, a display 14, a mechanism 15 for optionally moving the fixed mirror4 in the optical-axial direction. The mechanism 15 comprises asingle-axis translation stage mechanism 15A, a coupling mechanism 15B,and a pulse motor 15C. Reference letter A designates an object to beexamined.

Light from the SLD light source 1, which is a low-coherence lightsource, is split by means of the half mirror 2 into object light towardsthe object A to be examined and also into reference light. The referencelight, which is one of the two-split light beams, is guided to the firstmirror 3A and the second mirror 3B, which are contained in the lightdelay mechanism 3, and the fixed mirror (scanning-starting pointadjusting mirror) 4. The light is reflected at and returns from thefixed mirror 4 to the half mirror 2 via the same optical path.

On the other hand, the object light, which is the other of the two-splitlight beams, is guided through the plane scanning mechanism (X-axisscanning mirror and Y-axis scanning mirror) 5, the dichroic mirror 6,and the objective lens 7 to be made incident upon the object A to beexamined. The reflected light is caused to return to the half mirror 2via the same optical path.

In the light delay mechanism 3, a plurality of pairs of mirrors eachcomprising the first mirror 3A and the second mirror 3B are arranged onthe rotation member 12, which is rotated at high speed, in a radialpattern in such a manner that the light is reflected in the tangentialdirection of the rotation member 12.

The rotation member 12 is rotated at high speed. When the referencelight from the half mirror 2 propagates along the optical path from thehalf mirror 2, through the first mirror 3A, the second mirror 3B, thefixed mirror (scanning-starting point adjusting mirror) 4, the secondmirror 3B and the first mirror 3A, to the half mirror 2, the firstmirror 3A and the second mirror 3B move the optical path in the forwarddirection or in the backward direction due to the rotation of therotation member 12. Thus, the reference light is Doppler-frequencyshifted to the UV side or the infrared side. The above-describedheterodyne interference beat signal is generated correspondingly to thisDoppler-frequency shift.

With the above-described configuration, the length of the optical pathcan be optionally selected within the range where the reference lightcan be applied along the optical path as described above, and can bemade to correspond to the object light in the depth direction (Zdirection) of the optical axis. Thus, the reflection structure of a deeplayer of the object A to be examined can be scanned in the depthdirection.

Generally, in the plane scanning mechanism (X-axis scanning mirror andY-axis scanning mirror) 5, the mirrors fixed to the rocking portions ofdevices named galvanometers, which carry out rocking-motion at highspeed and with high accuracy, are arranged for the X-axis scanning andthe Y-axis scanning, respectively. The galvanometers for the X- andY-axis scanning are synchronously controlled, so that the X-Y plane isscanned with the object light reflected from the mirrors.

Substantially all of the light (infrared rays) from the SLD light source1 is passed through the dichroic mirror 6 to propagate toward the objectA to be examined. Substantially all of the light (visible light) fromthe CCD illumination light source 9 is reflected from the dichroicmirror 6 and propagate toward the object A to be examined. Moreover, ofthe light reflected from the object A to be examined, nearly all of theinfrared rays (signal component) are passed through the dichroic mirror6 to propagate toward the light detector 11. Of the light reflected fromthe object A to be examined, substantially all of the visible light(real picture component) is reflected from the dichroic mirror 6 topropagate toward the monitor CCD 10.

The half mirror 8 for the camera light source and the CCD illuminationlight source 9 are used to illuminate the object A to be examined when areal picture of the object A is taken by the monitor CCD 10.

The monitor CCD 10 captures the real picture of the object A to beexamined.

The reference light and the object light returning to the half mirror 2are combined with each other, and are supplied to the light detector 11.The reference light and the object light are combined to becomeinterference light, due to the interference phenomena of light waves, sothat beats are generated. In this case, when the length of the opticalpath from the half mirror 2 to the fixed mirror (scanning-starting pointadjusting mirror) 4 is equal to the length of the optical path from thehalf mirror 2 to the object A to be examined, a heterodyne interferencebeat signal is generated in the combined interference light. Theheterodyne interference beat signal is converted to an electrical signalin the light detector 11, and is supplied to the PC (personal computer)13.

The PC 13 carries out three-dimensional image-processing of theheterodyne interference beat signal, and a cross-sectional picture ofthe object A to be examined is displayed on the display 14.

Referring to the first mirror 3A and the second mirror 3B, right-angleprisms, corner-cube reflectors for three-plane reflection, Littrowreflectors, and cat's eyes may be used, in addition to thesurface-reflection mirrors arranged at a right-angle to each other,which is the simplest arrangement.

Moreover, a half-mirror may be installed in the optical path of theobject light, and the real surface of the object A to be examined isimaged by means of an image pickup device such as a CCD device or thelike. Thus, positioning of the optical axis for examination of theobject A to be examined can be easily performed.

Moreover, a mechanism 15 for optionally moving the fixed mirror 4 in theoptical-axis direction may be added, and thus, the scanning referenceposition in the depth direction (Z direction) can be optionally set.

As described above, according to the high-speed optical delay generatingmethod in optical coherence tomography of the present invention, thereference light from the half mirror 2 propagates along the optical pathfrom the half mirror 2, through the first mirror 3A, the second mirror3B, the fixed mirror (scanning-starting point adjusting mirror) 4, thesecond mirror 3B and the first mirror 3A, to the half mirror 2. That is,the reference light moves along the same optical path when it is madeincident and is reflected, and the light returns to the half mirror 2.Thus, the problem of the conventional high-speed optical delaygenerating method in optical coherence tomography, that is, the shift ofthe reflection optical axis from the incidence optical axis, does notoccur. Thus, heterodyne interference beat signals combined at the halfmirror 2 can be obtained at high speed over a very wide angular range.

Thus, according to the present invention, a cross-sectional picture witha sufficiently long scanning distance in the depth direction (Zdirection) can be provided.

Moreover, according to the present invention, high-precisioncross-sectional information can be taken at high speed over a wideangular range to be displayed. Thus, for example, when the presentinvention is applied to an ophthalmic disease diagnostic device, thediagnosis of eye-grounds, which has until now been conducted based onintuition and experience of ophthalmologists can be easily carried outat high speed and over a wide angular range.

Thus, eye-ground retinal diseases can be found early. Such diseases,which have been difficult to detect and cause the patients to lose theirsight, can be treated early for healing. This significantly reduces thephysical and mental burden of the patients.

The present invention is not restricted to the above-describedembodiments. Different modifications can be made based on the spirit ofthe present invention. It is to be noted that these modifications shouldnot be excluded from the present invention.

As described above in detail, according to the present invention, across-sectional picture having a sufficiently long scanning distance inthe depth direction (Z direction) can be obtained at high speed. Thatis, the reference light from the half mirror returns along the sameoptical path for both of the incident light and the reflection light.Thus, shifting of the reflection optical axis to the incidence opticalaxis, which is a problem of the conventional high-speed delay generatingmethod in optical coherence tomography, does not occur. Heterodyneinterference beat signals combined at the half mirror can be obtained athigh speed and over a wide angular range.

INDUSTRIAL APPLICABILITY

With the optical coherence tomography device of the present invention,high-precision cross-sectional information can be taken at high speedand over a wide angular range to be displayed. In particular, thisdevice is suitable for use as a medical diagnostic device such as anophthalmic disease diagnostic device.

1. An optical coherence tomography device comprising: (a) alow-coherence light source; (b) a two-splitting half mirror configuredto split light from the low-coherence light source into an object lighttowards an object to be examined and configured to split light from thelow-coherence light source into a reference light; (c) a light delaymechanism configured to delay the reference light by a rotationreflector; (d) a scanning-starting point adjusting mirror configured tocause the reference light from the light delay mechanism to be reflectedand returned to the delay mechanism; (e) a plane scanning mechanismconfigured to scan an inner plane of the object to be examined with theobject light; (f) an objective lens; (g) the two-splitting half mirrorconfigured to combine the object light returning from the object to beexamined with the reference light returning from the light delaymechanism; and (h) a light detector configured to detect interferencelight combined at the two-splitting half mirror; (i) wherein the lightdelay mechanism includes a plurality of pairs of mirrors each comprisinga first mirror and a second mirror arranged on the surface of a rotationmember, which is rotated in a radial direction so as to cause thereference light to be reflected in a tangential direction of therotation member; (j) wherein the scanning-starting point adjustingmirror is configured to adjust a scanning-starting point adjustingposition in the depth direction so as to correspond to the Z direction,which is the depth direction of the optical axis of the object light;and (k) wherein the plane scanning mechanism has an x-axis scanningmirror and a y-axis scanning mirror, and the x-y plane of the object tobe examined is scanned at high speed with the object light towards theobject to be examined; and further comprising (l) a dichroic mirrorconfigured to pass substantially all of the light from the low-coherencelight source to the object to be examined and configured to reflect asecond light from a second light source to a monitor.
 2. An opticalcoherence tomography device according to claim 1, wherein the object tobe examined is eyes.
 3. An optical coherence tomography device accordingto claim 1, wherein the plane scanning mechanism is configured to scanan eye.
 4. An optical coherence tomography device according to claim 1,wherein the second light source is a charge coupled device (CCD) lightsource.
 5. An optical coherence tomography device according to claim 1,wherein the monitor is a charge coupled device (CCD) monitor.
 6. Anoptical coherence tomography device according to claim 1, furthercomprising a half-mirror configured to split the second light from thesecond light source into a monitor light and a second object light sothat the object to be examined is illuminated when a real picture of theobject to be examined is taken by the monitor.